For Ron Shevlin, director of research at Cornerstone Advisors in Scottsdale, Ariz., a charter for a mobile-only fintech probably isn't a game-changer for credit unions, because the game has already changed.

"Look, if I'm a credit union CEO, I've got a list of problems … but honestly, Varo Money getting a charter doesn't put that any higher on my list of worries," he said. "Varo Money appearing on the scene in the first place, with all the others of their ilk – that's on my list of concerns because they're going after the same members or prospective members that I'm going after."

He added, "These firms like Varo Money, Chime, BankMobile, GoBank – all of these exist regardless of whether or not they have a charter. The threat is there regardless of what the legal status of the competitor is."

A lot of credit unions have bigger fish to fry right now, according to Shevlin. "The far bigger issue for credit unions to be worried about are the megabanks that are scooping up the millennial population," he said.

For Kalin Bornemann, a Seattle, Wash.-based attorney who advises credit unions and other financial institutions at law firm Miller Nash Graham & Dunn, however, cost pressure could be on the horizon. That's because charters could cut operating costs for fintechs, making it easier to win market share away from credit unions and traditional financial institutions, he said.

"A lot of those fintech companies are really operating under a state-by-state type landscape, which can get really expensive, because they have to get licensed in all those different states. So when you introduce this concept of a national bank charter, it eliminates the costs associated with it," he explained. "So then they can start saving costs on that angle and start dedicating it toward other pieces, if that's through lower rates or no-fee ATMs – those sorts of things."

Getting a charter isn't free, of course – the time and effort involved can be expensive, Shevlin noted.

"Then there are the compliance costs and issues going forward," he added. "I would assume that Varo did its homework and knows so that the cost of getting the charter and ongoing compliance is less than the cost of having to use a third party to, in effect, be its charter intermediary."

There are also the state regulators to think about, Allied Solutions Second VP of Digital Solutions Bill Haynes noted.

Operating costs are just the tip of the competitive iceberg, however. Chartering fintechs could put a bigger spotlight on credit unions' technological battles, too. Fintechs are intrinsically tech-savvy businesses, and many of them take a more expansive view of the market than some credit unions do, Haynes noted.

"You're not competing against Chase; you're not competing against even the big, big community regional banks," he explained. "You're competing against Amazon and you don't know it yet."

Bornemann added, "I think fintech banks might have an advantage because they have a lot of resources that they can dedicate toward having, really, the best technology. And some smaller credit unions I think recently have struggled in this space because they just don't have the resources or the budget that they can throw at having the best technology. It'll definitely be an area of focus for all credit unions if they want to stay competitive."

Despite the potential cost and technology advantages that some fintechs might gain with a charter, credit unions may still have a leg up with many consumers.

"You still have the relationships," Haynes said. "It's still people's money and … even though everybody is accepting of doing everything electronically, I still believe there's a little bit of that need for a relationship when it comes to your money."

People are also attracted to the social goals many credit unions have, Bornemann added.

"They really join a credit union because not only can they offer those great rates, products and services, but they also play a meaningful role in their communities through things like charitable and volunteer activities," he said.

Giving a charter to a fintech firm may redefine the flow of products and services, but don't get carried away, Shevlin warned.

"The whole notion that, 'Well, a mobile-only bank redefines what banking is,' it just seems to be so misguided," he said. "It's still the same damn product. It's still the same damn service. It's just that the communication and delivery mechanisms are a little bit different."

And credit union members will probably benefit from having chartered fintechs in the mix, even if the credit unions themselves are unsure of what the future will hold, Haynes said.

"I think ultimately the consumers win, and so I don't think that that can be a bad thing," he noted. "It also can provide that competition. And competition ultimately, aside from necessity, is probably the biggest driver of innovation."